1. Field
The embodiments discussed herein are directed to address learning of switches that have multiple-stage relation of connection.
2. Description of the Related Art
A network topology illustrated in FIG. 1 may be used to connect switches in a multistage configuration as in FAT tree. Referring to FIG. 1, a network may be connected in a two-stage configuration and includes lower stage leaf switches SW1 through SWm and upper stage root switches SW through SWn. Each of the leaf switches is respectively connected to each of the root switches SW1 through SWm. Each of the leaf switches may be connected to each of the terminal devices of any number. Referring to FIG. 1, k1 terminal devices T(1-1) through T(1-k1) are connected to the leaf switch SW1. The remaining leaf switches are simply not illustrated, and each of the remaining leaf switches SW1 through SWm may be connected to a total of k terminal devices.
A packet may be transmitted from the terminal device T(1-1) to the terminal device T(m-km) in such a network, for example. The leaf switch SW1 receives the packet from the terminal device T(1-1), and then transfers the packet to the root switch SWm. The root switch SW1 transfers the received packet to the leaf switch SWm. The leaf switch SWm outputs the packet to the terminal device T(m-km). Since the network illustrated in FIG. 1 is redundant, the leaf switch SW1 may transfer the packet to any of the root switches. To distribute workload, the transfer destination of the packet may be limited to the root switch SW1, for example. If a plurality of root switches can transfer packets to the terminal device T(1-1), the plurality of root switches need to learn an address of the terminal device T(1-1) in order to avoid flooding. In other words, the root switches SW1 through SWn need to hold the address of the terminal device in a redundant fashion. The root switches SW1 through SWn thus need to store a large number of addresses as terminal devices increase in number. A memory capacity of each root switch is subject to a limitation, which in turn limits the number of terminal devices.
A switching hub configured as discussed below is available to reduce the capacity of an address table. The switching hub includes a plurality of terminal communication local-area network (LAN) ports, and switching communication LAN ports, a switching controller for controlling switching of a plurality of terminals, a virtual LAN (VLAN) controller for separating a LAN into a plurality of networks according to setting, and an address table manager for managing an address table within a switch. The switching hub connects a plurality of LANs that use carrier sense multiple access/collision detection (SCMA/CD) as an access control protocol for a transfer medium. The switching hub performs concurrently a relay operation on the ports, and divides the LAN into a plurality of networks. The switching hub further includes an inter-switch address manager for distributing an address table in a VLAN among the switches, a VLAN ID processor for adding to or deleting from a relay frame an ID identifying which of the VLANs a frame belongs to, and an intra-VLAN transfer processor for transferring a frame within the same VLAN. Such a switching hub is effective in a cascade connected configuration, but not effective in the network illustrated in FIG. 1.